Additional file 8: Thickening fraction at end-expiration of the expiratory abdominal muscles is expressed in percentage (%). Patients are divided in 3 groups according to the change in expiratory muscles thickness during the first 4 days of MV. The number of patients with changes in thickness of >10% decrease, ≤10% change or with >10% increase in thickness for the different muscles’ groups were as follow: 15, 12, 7 (total expiratory muscles); 12, 9, 13 (OE), 16, 12, 6 (OI); 17, 6, 11 (TA); 4, 15, 15 (RA). OE = m. obliquus externa, OI = m. obliquus interna, TA = m. transversus abdominis, RA = m. rectus abdominis, MV = mechanical ventilation.